THE OCCIPITAL BONE 71 



The superior curved line gives attachment internally to the Trapezius, externally 

 to the muscular origin of the Occipitofrontalis, and to the Sternomastoid to the 

 extent shown in Fig. 39; the depressions between the curved lines to the Corn- 

 plexus internally, the Splenius capitis and Obliquus capitis superior externally. 

 The inferior curved line and the depressions below it afford insertion to the Rectus 

 capitis posticus, major and minor. 



The foramen magnum (foramen occipitale magnuin) is a large, oval aperture, 

 its long diameter extending from before backward. It transmits the lower por- 

 tion of the medulla oblongata and its membranes, the spinal part of the spinal 

 accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, 

 and the occipitoaxial ligaments. Its back part is wide for the transmission of 

 the medulla oblongata, and the corresponding margin rough for the attachment 

 of the dura enclosing it; the fore part is narrower, being encroached upon by the 

 condyles; it has projecting toward it, from below, the odontoid process, and its 

 margins are smooth and bevelled internally to support the medulla oblongata. 

 On each side of the foramen magnum are the condyles for articulation with the 

 atlas. Each condyle (condylus occipitalis] is convex, oval, or reniform in shape, 

 and directed downward and outward. The condyles converge in front, and 

 encroach slightly upon the anterior segment of the foramen. On the inner border 

 of each condyle is a rough tubercle for the attachment of the ligaments (check] 

 which connect this bone with the odontoid process of the axis; while external to 

 them is a rough tubercular prominence, the transverse or jugular process (processus 

 jugularis), channelled in front by a deep notch (incisura jiigularis}, which forms 

 part of the jugular foramen (foramen lacerum poster ius). The under surface of 

 this process presents an eminence (processus intrajuyularis], which represents the 

 paramastoid process of some mammals. The eminence is occasionally large, and 

 extends as low as the transverse process of the atlas. This surface affords attach- 

 ment to the Rectus capitis lateralis muscle and to the lateral occipitoatlantal 

 ligament; its upper or cerebral surface presents a deep groove, which lodges part 

 of the lateral sinus, while its external surface is marked by a quadrilateral rough 

 facet, covered with cartilage in the fresh state, and articulating with a similar 

 surface on the petrous portion of the temporal bone. On the outer side of each 

 condyle, near its fore part, is a foramen, the anterior condylar foramen (canalis 

 hypoglossi); it is directed downward, outward, and forward, and transmits the 

 hypoglossal nerve, and occasionally a meningeal branch of the ascending pharyn- 

 geal artery. This foramen is sometimes double. Behind each condyle is a 

 fossa 1 (fossa condyloideus), sometimes perforated at the bottom by a foramen, 

 the posterior condylar foramen (canalis condyloideus), for the transmission of a 

 vein to the lateral sinus. The basilar process (pars basilaris] is a strong quadri- 

 lateral plate of bone, which is wider behind than in front, and is situated in front 

 of the foramen magnum. Its under surface is rough, presents in the median line 

 a tubercular ridge, the pharyngeal spine (tuberculum pharyngeuni), for the attach- 

 ment of the tendinous raphe and Superior constrictor of the pharynx, and on each 

 side of it rough depressions for the attachment of the Rectus capitis anticus, 

 major and minor. 



The internal surface (Fig. 40) is deeply concave. The posterior part is divided 

 by a crucial ridge into four fossae. The two superior fossae receive the occipital 

 lobes of the cerebrum, and present slight eminences and depressions corresponding 

 to their convolutions. The two inferior, which receive the hemispheres of the 

 cerebellum, are larger than the former, and comparatively smooth ; both are marked 

 by slight grooves for the lodgement of arteries. At the point of meeting of the four 



1 This fossa presents many variations in size. It is usually shallow, and the foramen small; occasionally 

 wanting on one or both sides. Sometimes both fossa and foramen are large, but confined to one side only; more 

 rarely, the fossa and foramen are very large on both sides. 



